The login procedure of the HTTP API calls takes the most time. HTTP calls without the username and password are much faster than calls with the username and password.

If you do not need the security, for instance when you only send the messages from the local server, you can set the option 'Enable anonymous HTTP API requests' in the 'HTTP server' settings of the Web Connector to allow HTTP calls without the username and password parameters.

The HTTP API in Diafaan SMS Server does not support batch messages. It is possible to send the same message text to multiple numbers in one HTTP call but if you want to send a different message to multiple numbers you have to make one HTTP call per message.